This invention is directed to an electronic timepiece having a main oscillator circuit and a secondary oscillator circuit, and in particular to electronic timepiece circuitry for measuring a phase difference between high frequency time standard signals, produced by respective first and second oscillator circuits caused, at least in part, by temperature characteristics of the time standard utilized in the respective oscillator circuits, and for utilizing the phase difference to adjust the frequency rate of the timekeeping circuitry.
One problem that insures to electronic timepieces utilizing a piezoelectric vibrator as a time standard is the variation in the frequency rate of the vibrator casued by the temperature characteristics thereof. Although oscillator circuits have been provided with capacitors, having a temperature characteristic similar to that of the piezoelectric vibrator, at best, such capacitors can only approximate the temperature characteristic of the quartz crystal vibrator and, hence, cannot completely compensate therefor. Even though piezoelectric vibrators, capable of vibrating at very high frequencies, such as in the mega-Hertz range, vary little in response to temperature changes, these high frequency vibrators have been found to be less than completely satisfactory in electronic timepieces. Specifically, such high frequency piezoelectric vibrators are extremely large, thereby rendering it different to miniaturize the electronic timepiece. Secondly, by providing a time standard signal in the mega-Hertz range, the timekeeping circuitry is required to operate at higher switching speeds, thereby consuming an excess of power, and hence shortening the life of the battery utilized to power the electronic wristwatch. Accordingly, a small size electronic wristwatch, having first and second piezoelectric vibrator time standards for reducing variations in the timing rate caused by the temperature characteristics of the respective time standards, is desired.